Heaviness of western rowing crew (6)
I believe the answer is:
weight
'heaviness' is the definition.
(I've seen this before)
'western rowing crew' is the wordplay.
'western' becomes 'w'.
'rowing crew' becomes 'eight' (I've seen this before).
'w'+'eight'='WEIGHT'
'of' acts as a link.
(Other definitions for weight that I've seen before include "Vertical force exerted by a mass" , "Gravitational pull" , "The property of heaviness, measure of mass" , "Burden" , "Significance" .)